Report of construction defects, no response, next step?!?

It is not about an amount, or rather I don’t know it yet, since no other company has plastered it so far. By law, after the deadline has passed, I have the choice whether to grant another deadline or have the defect fixed externally. After that, I would probably have to sue for the costs. If I go directly to a lawyer now, that will cost me money, in addition to the costs of having the garage plastered.... the costs of which I would then also have to sue for.....

So what to do, said Zeus?!?

Phew,
is a defect notification equivalent to a reminder? Then one probably has to write again, right???
Why does no one answer the phone there? What kind of company is it? Do they have an office or is it a smaller outfit that only works with a cell phone and can only call back because they are usually working on a construction site?
I would show up there in person.
A lawyer is all well and good, but should be the last resort before trying all other options. After all, a lawyer also costs something.

If you have already paid everything, then the only option left is to take legal action?

It is a very large garage company operating nationwide in Germany, the name can be given gladly via PM, as they have already issued me a warning because of a bad review. The fact that they are not finishing the garage is a spiteful reaction to an impending lawsuit on our part. It concerns another order that they cannot execute as ordered, but want to keep the deposit as a planning fee.

Is there a warranty bond? Then extend the deadline again, if nothing happens, pay for the defect remediation from the bond. If there is no bond, appeal to the company's goodwill and hope...

You must at least set a deadline for complete delivery. A notice of defects is rather not the right way. Formally speaking, in my opinion, this is not a defect.

If you complete the garage now at your own expense, you will never get anything from the garage company.